This proposal concerns studies of the retina as a model system of a neural tissue and as a system for the study of biochemical control mechanisms in this tissue. Glutamine Synthetase (GS) and other enzymes, and their possible relation to the visual function of the retina, as well as general retinal metabolism, are a major focus. GS, which is present in high concentrations in neural retina, can be prematurely induced in embryonic chick retina by glucocorticoids; the role of steriod receptors and cell-cell interaction in the inductive process are being studied, as is the inhibition of the induction by L-glutamate and several analogues. L-glutamate severely damages embryonic and neonatal retina both in vivo and in culture. The primary emphasis of the current and future work is to attempt to elucidate the biochemical and morphological effects of monosodium glutamate on retinal tissue. We are investigating the age dependence of this effect; effects oo glutamate analogues, and effects of time and concentration of treatment on severity of the effect. Localization of glutamate, as well as GS in the retina, are also under investigation.